The present invention is directed to probe structures for testing of electrical interconnections to integrated circuit devices and other electronic components and particularly to testing integrated circuit devices with flat or recessed surfaces for wired bonded interconnections.
Integrated circuit (IC) devices and other electronic components are normally tested to verify the electrical function of the device and certain devices require high temperature burn-in testing to accelerate early life failures of these devices. The various types of interconnection methods used to test these devices include permanent, semi-permanent, and temporary attachment techniques. The permanent and semi-permanent techniques that are typically used include soldering and wire bonding to provide a connection from the IC device to a substrate with fan out wiring or a metal lead frame package. The temporary attachment techniques include rigid and flexible probes that are used to connect IC device to a substrate with fan out wiring or directly to the test equipment.
The permanent attachment techniques used for testing integrated circuit devices such as wire bonding to a leadframe of a plastic leaded chip carrier are typically used for devices that have low number of interconnections and the plastic leaded chip carrier package is relatively inexpensive. The device is tested through the wire bonds and leads of the plastic leaded chip carrier and plugged into a test socket. If the integrated circuit device is defective, the device and the plastic leaded chip carrier are discarded.
The semi-permanent attachment techniques are typically used for testing integrated circuit devices with solder ball attachment to a ceramic or plastic pin grid array package. The device is tested through the solder balls and the internal fan out wiring and pins of the pin grid array package that is plugged into a test socket. If the integrated circuit device is defective, the device can be removed from the pin grid array package by heating the solder balls to their melting point. The processing cost of heating and removing the chip is offset by the cost saving of reusing the pin grid array package.
The most cost effective techniques for testing and burn-in of integrated circuit devices provide a direct interconnection between the pads on the device to a probe socket that is hard wired to the test equipment. Contemporary probes for testing integrated circuits are expensive to fabricate and are easily damaged. The individual probes are typically attached to a ring shaped printed circuit board and support cantilevered metal wires extending towards the center of the opening in the circuit board. Each probe wire must be aligned to a contact location on the integrated circuit device to be tested. The probe wires are generally fragile and easily deformed or damaged. This type of probe fixture is typically used for testing integrated circuit devices that have contacts along the perimeter of the device. This type of probe is also much larger that the IC device that is being tested and is limited to testing a single IC device at a time.
Another technique used for testing IC devices uses a thin flex circuit with metal bumps and fan out wiring. The bumps are typically formed using photolithographic processes and provide a raised contact for the probe assembly. The bumps are used to contact the flat or recessed wire bond pads on the IC device. An elastomer pad is typically used between the back of the flex circuit and a pressure plate or rigid circuit board to provide compliance for the probe interface. This type of probe is limited to flexible film substrate materials that typically have one or two wiring layers. Also, this type of probe does not provide a wiping contact interface to ensure a low resistance contact. The prior art described below includes a variety of different probe fixtures for testing bare IC chips.
1. U.S. Pat. No. 5,172,050, issued Dec. 15, 1992 to Swapp is directed to fixtures for testing bare IC chips. The fixture is manufactured from a silicon wafer or other semiconductor substrate material. The probe contacts are fabricated in the top surface of the substrate using micromachining techniques. Each probe contact is formed by etching a cavity into the substrate with a cantilevered beam extending into the center of the cavity. The minimum spacing and density of the probe contacts is limited by the need to use the space between the contacts for fan out wiring and the diameter of the cavities must be larger than the contact pad on the IC device to allow the cantilever beam contacts to flex. Although this technique is similar to the probe structure described in this patent application, it is limited to substrates made from a silicon wafer or other semiconductor materials.
2. U.S. Pat. No. 5,177,439, issued Jan. 5, 1993 to Liu et al., is directed to fixtures for testing bare IC chips. The fixture is manufactured from a silicon wafer or other substrate that is compatible with semiconductor processing. The substrate is chemically etched to produce a plurality of protrusions to match the I/O pattern on the bare IC chip. The protrusions are coated with a conductive material and connected to discrete conductive fan out wiring paths to allow connection to an external test system. The probes described in this patent are rigid and do not provide a wiping interface with the mating contacts on the IC device. Also, the substrate used for fabrication of this probe fixture is limited to semiconductor wafers which are relatively expensive. The high density cantilever test probe can be fabricated on a variety of inexpensive substrate with the fan out wiring.
3. U.S. Pat. No. 5,635,846 describes a high density test probe for integrated circuit devices. The probe structure described in this docket uses short metal wires that are bonded on one end to the fan out wiring on a rigid substrate. The wires are encased in a compliant polymer material to allow the probes to compress under pressure against the integrated circuit device. The wire probes must be sufficiently long and formed at an angle to prevent permanent deformation during compression against the integrated circuit device. High temperature applications of this type of probe are limited due to the glass transition temperature of the polymer material surrounding the probes as well as the coefficient of thermal expansion mismatch between the compliant polymer material and the rigid substrate.
It is the object of the present invention to provide a probe for testing integrated circuit devices and other electronic components that use flat or recessed surfaces for wire bonded interconnectors.
Another object of the present invention is to provide a probe structure that is an integral part of the fan out wiring on the test substrate or other printed wiring means to minimize the electrical conductor length as well as the contact resistance of the probe interface.
A further object of the present invention is to provide a raised probe tip for contacting recessed surfaces on the IC device.
An additional object of the present invention is to provide a compliant probe structure that has a wiping interface as the probe is compressed against the mating contacts on the IC device.
Yet another object of the present invention is to provide a fabrication process that minimizes the potential for damaging the interconnect circuit wiring in the substrate material.
Yet an additional object of the present invention is to provide a high density probe structure to allow multiple chips to be tested by a single test fixture.